1. Technical Field
The present invention relates to a structure of a piston ring that is configured to be installed in an engine and has a matrix with a laminated intermediate layer coated on a surface of the matrix and a diamond-like carbon film coated on an outer periphery of the intermediate layer. Thus, the piston ring is wrapped by a skin with a progressive structure having a gradient distribution of hardness. The structure formed from the diamond-like carbon film provides expected low wear rate and low friction coefficient, while applying a high bonding force to the matrix and making the piston ring have a long service life as the related environmental regulations require.
2. Description of Related Art
The conventional piston for being installed in a vehicle engine typically has two to three serially arranged frictional components (i.e. a compression ring, an oil ring, and a scraper ring, generally known as piston rings). The scraper ring is in the shape of a thin ring and is mounted around the piston to closely contact the inner wall of the cylinder, to prevent the engine oil within the cylinder from upward flowing to the combustion chamber. The inner wall of the cylinder is covered by a layer of oil that is supplied by the oil ring. During air intake and power strokes of the engine, the scraper ring serves to remove excess engine oil from the inner wall of the cylinder. The existing scraper ring, however, is limited in the overall structural strength and elasticity, so it tends to wear out prematurely and has a reduced service life. When the scraper ring having such poor structural strength and elasticity and coming without any special surface treatment is worn after a period of use, the consumption of engine oil is increased, so that the engine starts to waste engine oil. In addition, poor air-tightness of the piston can decrease the combustion efficiency, and in a worse case, the piston can move unstably, thereby hindering the engine from supplying power smoothly.